1. Field of Invention
The present invention relates to a Micro-Electro-Mechanical System (MEMS) pressure sensor device and a manufacturing method thereof; particularly, it relates to such MEMS pressure sensor device and manufacturing method capable of sensing a lower pressure.
2. Description of Related Art
FIGS. 1A-1E show cross-section views of a manufacturing flow of a MEMS pressure sensor device disclosed by U.S. Pat. No. 6,093,579. As shown in FIG. 1A, by a first lithography process, a region 104 is defined on a substrate 100 by a mask 102 and a mask 106, wherein the mask 102 covers the rest of the substrate 100 and the mask 106 has a specific pattern to define the pattern of the region 104. FIG. 1B is a schematic cross-section view showing the MEMS pressure sensor device after the first lithography process and a first etching process. As shown in FIG. 1B, after the first etching process, a membrane (the substrate) of the MEMS pressure sensor device includes a boss 108 with the specific pattern in the center area and deep trenches 110 around the boss 108, wherein the boss 108 has a thickness d. Next, as shown in FIG. 1C, a second lithography process is performed wherein the boss 108 is no longer covered by the mask 106, and a second etching process is applied to obtain a desired thickness of the membrane, wherein the thickness d of the boss 108 is relatively maintained. In the second etching process, the trapezoid boss 108 is rounded at edges as shown by the cross-section view in FIG. 1D. At last the mask 102 outside the region 104 is removed, such that a thinner membrane with the boss 108 is obtained as shown in FIG. 1E.
A membrane with the boss 108 and having a thinner thickness causes the MEMS pressure sensor device to have a relatively higher sensitivity and a relatively wider linear operation region. However, although this prior art can generate a MEMS pressure sensor device with such a membrane, it requires two lithography processes and the second lithography process must be aligned with the first lithography process. After the trenches 110 are formed, the topography of the substrate 100 is rugged and this is very disadvantageous to the second lithography process. The alignment may fail, and specific process and material maybe required. Therefore, this prior art needs relatively high manufacturing cost.
Besides, the second etching process is an anisotropic etching process. The boss 108 will be squared from a top view (not shown) after the anisotropic etching process; this is due to the characteristics of the anisotropic etching and the lattice of the substrate 100. Therefore, this prior art limits the shape of the boss 108 and therefore limits the design and application of the MEMS pressure sensor device.
In view of above, to overcome the drawbacks in the prior art, the present invention proposes a MEMS pressure sensor device and a manufacturing method thereof, which can sense a lower pressure with a lower manufacturing cost so as to provide wider applications.